Electromotive vehicles such as electric passenger cars, electric golf carts and electric forklift trucks, for instance, rely on an electric drive motor to acquire the torque needed to move forwards or backwards. Taking the electric forklift truck as an example, it employs a buttery-driven electric motor which can rotate with a controlled torque and in a controlled direction. The direction of rotation of the electric motor is controlled by a direction control lever swingably mounted on one side of a truck console. The direction control lever is hand-operated to shift between a forward position, a neutral position and a reverse position. Cooperating with the direction control lever are forward and reverse microswitches coupled to a microprocessor that, in response to the electric signals supplied from the microswitches, controls the flow of electric current to the electric motor. The forward microswitch becomes active to feed forward drive signals to the microprocessor when the direction control lever is shifted into the forward position, whereas the reverse microswitch is rendered active to feed reverse drive signals to the microprocessor if the direction control lever is swung into the reverse position. The forward and reverse microswitches remain inactive, when the direction control lever is in the neutral position, to have the microprocessor cease the electricity supply to the electric motor.
In the meantime, the acceleration of the electric motor employed in the electric forklift truck depends on the swing angle of a foot-operated accelerator pedal depressibly mounted on the floor of the forklift truck. The accelerator pedal is normally biased by a tension spring into an initial position in which the electric motor produces little or no torque. As the swing angle of the accelerator pedal grows larger, the torque produced by the electric motor is progressively increased such that the forklift truck can move at an accelerated speed. Such acceleration of the electric motor is controlled by way of detecting the variation of the pedal swing angle and regulating the amount of electric current to be supplied to the electric motor. The task of detecting the swing angle variation has heretofore been carried out either by means of photoelectric sensors which are arranged to become active one by one and to generate digital signals corresponding to the pedal swing angle, or a potentiometer which is designed to measure the electromotive forces induced by the swinging movement of the pedal and to generate analog signals corresponding to the electromotive forces. The digital or analog signals are fed to the microprocessor which in turn functions to regulate the current supply amount to the electric motor to thereby control the torque and speed of the latter.
As referred to above, the direction of rotation and the acceleration of the forklift electric motor are controlled by the microprocessor in response to the input signals fed from the microswitches associated with the direction control lever and the photoelectric sensors or the potentiometer associated with the accelerator pedal. According to the prior art accelerator device, however, a drawback is noted in that the acceleration signal generator mechanism is highly susceptible to water intrusion, water damage and bearing/seal wear, which may be a major culprit of causing failure of the accelerator device. Another shortcoming of the prior art accelerator device is that the acceleration signal generator mechanism is of costly and complicated structure mainly because it lies under the vehicle floor in a position remote from the microprocessor.